Invoking Step Functions from Lambda

handler.py

import json
import boto3

sfn = boto3.client('stepfunctions')

def lambda_handler(event, context):
  sfn_st = "arn:aws:states:ap-southeast-2:123456789:stateMachine:StepFunctionArn"
  data = []
  for unicorn in unicorns_to_feed:
    obj = {}
    obj["id"] = unicorn['id']
    obj["last_fed"] = unicorn['last_fed']
    data.append(obj)

  sfn_input = {}
  sfn_input["UnicornsToFeed"] = data
  sfn_input = json.dumps(sfn_input)
  
  start_execution_response = sfn.start_execution(
    stateMachineArn=sfn_st,
    input=sfn_input
  )

  response={}
  response['executionArn'] = start_execution_response['executionArn']

  return {
    'statusCode': 200,
    'body': json.dumps(response)
  }